The Wireless HD 1.0 standard defines a wireless video area network (WVAN) for the connection of consumer electronic (CE) audio and video devices. A key attribute of the WirelessHD system is its ability to support the wireless transport of an uncompressed 1080p A/V stream with a high quality of service (QoS) within a room at distances of ten meters.
The requirement for high data throughput at distances of 10 meters requires a large allocated frequency spectrum. A large amount spectrum is available on an unlicensed basis in many countries in the 60 GHz band. In North America and Japan, a total of 7 GHz is allocated for use, 5 GHz of which is overlapping. The band 57˜64 GHz is allocated in North America while 59-66 GHz is allocated in Japan. In addition, Korea and the European Union have also allowed similar allocations. The regulator agencies allow very high effective transmit power (the combination of transmitter power and antenna gain), greater than 10 W of effective isotropic radiated power (EIRP). High EIRP and wide allocated bandwidth will allow high throughput connections that, however, are very directional.
The WirelessHD 1.0 specification defines a wireless protocol that enables directional connections that adapt very rapidly to changes in the environment. This is accomplished by dynamically steering the antenna beam at the transmitter while at the same time focusing the receiver antenna in the direction of the incoming power from the transmitter. This dynamic beam forming and beam steering utilizes not only the direct path, but allows the use of reflections and other indirect paths when the line-of-sight connection is obstructed. This dynamic adjustment of the antenna energy is completed in less than one millisecond.
The WVAN includes one Coordinator and zero or more Stations. The Coordinator schedules time in the channel to ensure that the wireless resources are prioritized for the support of A/V streams. The other devices that are a part of the WVAN are referred to as Stations. A station may be the source and/or sink of data in the network. The device that is the Coordinator also acts as a Station in the WVAN and may act as a source and/or sink of data. <http://www.wirelesshd.org/technology.html>
Most image compression schemes are designed for “natural images” such as photos taken by a digital camera. For natural images, strong correlation exists among neighboring pixels. Hence, most image compression schemes work as follows:
1. The pixels are decorrelated using prediction or transform or both, resulting in a sparse histogram of the prediction residuals or transform coefficients. The histogram has a single peak which is located around 0.
2. Quantization is applied as necessary.
3. The (quantized) prediction residuals or transform coefficients are entropy coded. The entropy coder is designed for distributions described above. If the distribution has a significantly different shape, the coding performance is able to be poor.
However, there are many “unnatural images” such as images of graphics or text which typically have a large dynamic range, strong contrast, sharp edges, strong textures and sparse histograms. These types of images are usually not handled well by conventional image compression algorithms. Inter-pixel correlation is weaker, and prediction or transform does not provide a sparse distribution as it does for natural images.
Some schemes have been proposed for unnatural images. One example is referred to as “histogram packing” where the encoder goes through the whole image, computes the histogram and does a non-linear mapping of the pixels before compressing the image. The compression requires a two-pass processing, causing increased memory cost and more computations. The bitstream is not scalable which means that the decoder needs the whole bitstream to decode the image. Partial reconstruction is not possible without re-encoding.